This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2002-15860, filed Jan. 24, 2002; and No. 2002-184604, filed Jun. 25, 2002, the entire contents of both of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a toner supply roller used in an image forming apparatus of a toner developing system such as a copying machine, a facsimile machine or a laser beam printer.
2. Description of the Related Art
An image forming apparatus of a toner developing system comprises in general a photosensitive drum, an electrostatic latent image forming means for forming an electrostatic latent image on the photosensitive drum, a developing roller rotated in direct contact with or close to the photosensitive drum, a toner supply roller for supplying toner to the developing roller, and a toner regulating member for regulating the toner supplied onto the developing roller to a uniform thickness. Fist, an electrostatic latent image is formed on the surface of the photosensitive drum by the electrostatic latent image forming means, based on prescribed picture image information. On the other hand, toner is supplied onto the surface of the developing roller by the toner supply roller. The toner supplied onto the developing roller is regulated by the toner regulating member to a uniform thickness so as to form a thin toner layer of a uniform thickness on the surface of the developing roller. The developing roller having the thin toner layer of a uniform thickness formed on the surface permits the toner to be attached successively to the electrostatic latent image formed on the photosensitive drum in the nip portion, or in the vicinity thereof, between the photosensitive drum and the developing roller, thereby achieving toner development.
The toner supply roller used in the image forming apparatus of the toner developing system described above comprises a metallic core shaft and an electrically conductive elastic layer formed on the outer surface of the shaft. In the prior art, the conductive elastic layer has been formed by dispersing an electrically conductive carbon used as an electrically conductive material into a resin foam such as a polyurethane foam by kneading. However, in the case of preparing a toner supply roller having a generally required surface resistance of 106 to 1010 xcexa9 by using an electrically conductive carbon, the conductive carbon fails to be dispersed uniformly into the resin material. As a result, the surface resistance is rendered nonuniform depending on the lot, depending on the roller in the same lot, or depending on the site of the same roller. Thus, it has been difficult to manufacture a toner supply roller having a nonuniformity in the surface resistance lower than 10%.
Therefore, it is an object of the present invention to provide a toner supply roller comprising an electrically conductive elastic layer exhibiting a substantially uniform surface resistance.
According to a first aspect of the present invention, there is provided a toner supply roller comprising a core shaft and an electrically conductive elastic layer formed on a outer peripheral surface of the shaft, the conductive elastic layer comprising an open-cell polyurethane foam, wherein an electrically conductive polymer and a binder are attached to cell walls of the polyurethane foam.
According to a second aspect of the present invention, there is provided toner supply roller comprising a core shaft and an electrically conductive elastic layer formed on a outer peripheral surface of the shaft, the conductive elastic layer comprising an open-cell polyurethane foam, wherein an electrically conductive polymer and a binder are attached to cell walls of the polyurethane foam, and the polyurethane forming the polyurethane foam is exposed to the outer circumferential surface of the conductive elastic layer.
Further, according to a third aspect of the present invention, there is provided a method of manufacturing a toner supply roller, comprising impregnating a block of open-cell polyurethane foam with an impregnating solution containing an electrically conductive polymer and a binder, attaching the conductive polymer and the binder to cell walls of the polyurethane foam, followed by drying the impregnated polyurethane foam; inserting a core shaft into the block of dried polyurethane foam; and polishing the outer surface of the block of polyurethane foam so as to form a circumferential surface.
The conductive polymer used in the present invention may be selected from a polyaniline-based polymer, a polyaniline sulfonic acid-based polymer, a polypyrrol, a polyacetylene and a mixture thereof.
The binder used in the present invention may be selected from acryl-based resin such as an acrylic resin, a polyacrylic acid ester resin, an acrylic acid-styrene copolymer resin or an acrylic acid-vinyl acetate copolymer resin, a polyvinyl alcohol, a polyacrylamide, a polyvinyl chloride resin, a urethane resin, a vinyl acetate resin, a butadiene resin, an epoxy resin, an alkyd resin, a melamine resin, a chloroprene rubber and a mixture thereof.
In the present invention, it is desirable for the conductive polymer and the binder to be contained in the cells, and attached to the cell walls, of the polyurethane foam in a total amount of 5 to 18% by weight based on the weight of polyurethane foam. Also, it is desirable for the weight ratio of the binder to the conductive polymer to fall within a range of 0.1 to 10.
Additional objects and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention. The objects and advantages of the present invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.